1. Field of the Invention
The present invention relates to a retaining member. In particular, the present invention relates to a retaining member adapted in a metal-air cell and a cell unit utilizing the same.
2. Description of Related Art
A metal-air cell, such as a zinc-air cell includes a zinc anode, an air cathode and a separator. The anode contains materials to be oxidized while the cathode contains material to be reduced during the electrochemical reaction so as to generate electrical power. The OH− ion is transferred from the air cathode to the zinc anode through the alkali electrolyte, such as potassium hydroxide (KOH) solution.
The anode of the metal-air cell typically comprises a slurry-like material that contains metal powders, binder, and electrolyte. The metal powder can be zinc powder, magnesium powder, aluminum powder or the alloy powder thereof. When the metal powder reacts with the alkali electrolyte, gas (i.e., hydrogen) is often generated as byproduct of an accompanying side reaction. However, the above-mentioned reaction is undesirable due to its consumption of metal powder to form the oxidation thereof. As a result of the undesired consumption of metal powder, the discharge capacity of the cell is reduced. Furthermore, the production of the hydrogen gas increases the internal pressure of the cell. The increased pressure of the generated gas inside the cell is one of the major causes for electrolyte leakage. In other words, due to the increased pressure of the generated gas, the electrolyte will be leaked through the assembly gap on the casing (i.e., battery cartridge) or gaps formed in connector interfaces. As a result, the reliability of the cells may fall short in meeting the specified application requirements.
In conventional metal-air cell structures, the air cathode is a porous plate structure having through holes thereon so that the gas may pass the air cathode smoothly. In other words, the gas inside the cell may be exhausted from the porous air cathode through the separator. However, after the discharge or preservation, the formed metal oxide, such as the zinc oxide is deposited on the separator to block the exhaustion path of the gas. Thus, the generated gas inside the cell may not be exhausted smoothly due to the blocked separator and the pressure of the generated gas inside the cell is more increased. As discussion above, the increased pressure of the generated gas results in the problem of the electrolyte leakage.
One conventional solution to this problem is to provide venting holes on the battery cartridge for releasing the gas. However, in practice, the venting holes of the traditional cartridge structure are often blocked by the aqueous anode metal slurry due to vibration of the battery or unexpected storage orientation. In addition, the anode expansion/deformation as a result of the chemical reaction during battery discharge may also cause the blockage of the venting holes. As a result, the generated gas cannot be smoothly released and gathers inside the cartridge, thus still causing undesired electrolyte leakage.